Our goal is to understand the basic principles behind the bioacoustical and neurobehavioral bases of hearing and communication in insects, especially sound localization in the fly, Ormia ochracea Bloengineers are applying design principles we learned from Ormia to construct tiny, silicon-based directional microphones for hearing aids, a strategy known as "biomimicry." This has stimulated us to consider how the fly's ears perform acoustically under noisy conditions. The ears' design features, forged over evolutionary time, include enhanced signal-to-noise and directional sensitivity while maintaining high sensitivity. In Ormia. both biomechanical and neural systems possess innovative auditory adaptations for temporal processing that are worth investigating for their intrinsic interest, and that have implications for practical applications, as well.We propose a set of behavioral experiments using a new apparatus to measure: (1) The ability of masking noise to degrade phonotaxis; (2) The ability to discriminate front from back sound sources; (3) How elevational cues are used to localize sound; and (4) Whether Ormia has an ultrasound-initiated ultrasound startle response. We propose a set of neurophysiological studies in Ormia's auditory system to determine: (1) Directional properties of auditory interneurons in the CNS; (2) The role of neural inhibition in shaping the directional responses in auditory interneurons; (3) How directional information in auditory pathways is integrated with flight-related propnoceptive signals to produce coordinated movements which steer the fly toward a sound source; (4) Mechanisms of multi-modal integration in the brain: when auditory and visual signals are present in cooperation or in rivalry.We propose to investigate the substrate communication system of Salticid jumping spiders. These spiders are renowned for their extravagant visual displays which turn out to be perfectly coordinated with a newly-discovered set of acoustic signals. The courtship behavior of these spiders will be an ideal system for the neuroethological study of multi-modal communication.